|Publication number||US7427504 B2|
|Application number||US 10/667,639|
|Publication date||Sep 23, 2008|
|Filing date||Sep 22, 2003|
|Priority date||Nov 22, 2002|
|Also published as||US7339160, US7432109, US7993604, US8057752, US20040129874, US20040219064, US20060163467, US20090047181, US20090084175, WO2004048969A1|
|Publication number||10667639, 667639, US 7427504 B2, US 7427504B2, US-B2-7427504, US7427504 B2, US7427504B2|
|Inventors||Torleif Torgersen, Bhavani Raghuraman, Edward Harrigan, Oliver C. Mullins, Gale Gustavson, Philip Rabbito, Ricardo Reves Vasques|
|Original Assignee||Schlumber Technology Corporation|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (11), Non-Patent Citations (5), Referenced by (19), Classifications (17), Legal Events (5)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application claims priority to co-owned, co-pending GB patent application no. 0227267.2, to Raghuraman et al., “Apparatus and Method for Analysing Downhole Water Chemistry”, filed 22 Nov. 2002.
The invention is intended for use in the petroleum industry, or in any industry requiring the characterization of fluids residing downhole in a fluid reservoir in an earth formation surrounding a borehole.
In oil well evaluation, quantitative analyses of formation fluid are typically performed in a laboratory environment, the samples having been collected downhole and brought to the surface in the sample chamber of a wireline formation tester.
Standard laboratory procedures are available to do quantitative analyses by addition of a reagent that reacts chemically with a specific target species in a sample to cause detectible changes in fluid property such as color, absorption spectra, turbidity etc. See Vogel, A. I., “Text-Book of Quantitative Inorganic Analysis, 3rd Edition”, Chapter 10-12, John Wiley, 1961. Such changes in fluid property may be caused, for example, by the formation of a product that absorbs light at a certain wavelength, or by the formation of an insoluble product that causes turbidity, or bubbles out as gas. For example, addition of pH sensitive dyes is used for calorimetric pH determination of water samples. A standard procedure for barium determination requires addition of sodium sulfate reagent to the fluid sample resulting in a sulfate precipitate that can be detected through turbidity measurements. Some of these standard laboratory procedures have been adapted for flow injection analysis (Ruzicka, J. and Hansen, E. H., Flow Injection Analysis, Chapters 1 and 2, John Wiley, 1981). Flow injection analysis “is based on the injection of a liquid sample into a moving non-segmented continuous carrier stream of a suitable liquid” (Chapter 2, page 6).
Fluid samples collected downhole can undergo various reversible and irreversible phase transitions between the point of collection and the point of analysis as pressure and temperature conditions are hard to preserve. Concentrations of constitutive species may change because of loss due to vaporization, precipitation etc., and hence the analysis as done in the laboratories may not be representative of true conditions downhole. For example, water chemistry and pH are important for estimating scaling tendencies and corrosion; however, the pH can change substantially as the fluid flows to the surface. Scaling out of salts and loss of carbon dioxide and hydrogen sulfide can give misleading pH values when laboratory measurements are made on downhole-collected samples.
While downhole formation sampling tools are usually equipped with spectrophotometric detectors, currently there are no available methods to carry one or more reagents downhole and inject them into the flow-line to enable such an analysis.
A method for analyzing formation fluid in earth formation surrounding a borehole includes storing analytical reagent in a reagent container in a fluids analyzer in a formation tester and moving the formation tester, including the reagent, downhole. Reagent from the reagent container is injected into formation fluid in the flow-line to make a mixture of formation fluid and reagent. The mixture is moved through a spectral analyzer cell in the fluids analyzer to produce a time-series of optical density measurements at a plurality of wavelengths. A characteristic of formation fluid is determined by spectral analysis of the time-series of optical density measurements.
A method for determining fluid chemistry of formation fluid in earth formation surrounding a borehole includes storing analytical reagent in a reagent container coupled to a fluids analyzer via a flow-line in a formation tester, transporting the formation tester downhole, drawing formation fluid into the flow-line, moving a mixture of formation fluid and analytical reagent through a spectral analyzer cell in the fluids analyzer, and performing reagent injection spectral analysis on the mixture. Performing reagent injection spectral analysis includes injecting reagent into the flow-line to create a mixture of formation fluid and reagent in the flow-line. Preferably, the method further includes establishing and storing baseline optical density values for at least one wavelength prior to injecting reagent. Preferably, injecting reagent includes injecting a predetermined volume of reagent into formation fluid within the flow-line. Preferably, injecting reagent includes adjusting the predetermined volume. Preferably, adjusting the predetermined volume includes adjusting an injection period of time. Preferably, injecting reagent includes injecting reagent into a stopped formation fluid. Preferably, injecting reagent includes injecting reagent using a syringe pump.
Alternatively, adjusting the predetermined volume includes adjusting an injection pump rate.
Alternatively, injecting reagent includes injecting reagent into a flowing formation fluid.
Alternatively, injecting reagent includes injecting reagent using wellbore overpressure using a restrictor or a throttle valve.
Alternatively, injecting reagent includes extracting formation fluid from a stopped flow-line using a syringe pump, a flow-line pump, or a step piston.
A fluids analyzer for analyzing formation fluid in earth formation surrounding a borehole includes a probe for receiving downhole formation fluid from earth formation, a flow-line coupled to receive formation fluid downhole from the probe, a reagent container in fluid communication with the flow-line, spectral analyzer means coupled to receive a mixture of formation fluid and reagent from the flow-line downhole for analyzing the mixture to produce time-series optical density data at a plurality of wavelengths, and computing means for determining a characteristic of formation fluid from the optical density data. Preferably, the reagent container is a syringe pump.
Alternatively, the reagent container is exposed to wellbore pressure. Alternatively, a fluid container is coupled to extract fluid from the flow-line.
Optionally, a second reagent container is provided in communication with the flow-line independently of a first reagent container.
The present invention provides a method and apparatus for determining fluid chemistry of formation fluid in an earth formation surrounding a borehole. In particular, it provides a novel method and apparatus for delivering a suitable mixture of formation fluid and analytical reagent to a downhole spectral analyzer.
The above-mentioned priority document, patent application GB 0227267.2 discloses a method for analyzing downhole water chemistry. It discloses a general approach to analysis of water chemistry including details of the chemistry and the spectral analysis involved. This approach requires injecting a specific indicator or reagent into a sample of water and determining the resulting color of the fluid with an optical spectrophotometer. Patent application GB 0227267.2 is hereby incorporated herein by reference.
The present invention, in a preferred embodiment, also requires injecting reagent into a downhole sample of formation fluid, and discloses an apparatus and a method to do this. The present invention also discloses in detail a novel method for injecting reagent into formation fluid that may contain any of water, oil, and gas, to make a suitable mixture of formation fluid and analytical reagent for downhole spectral analysis. The method includes transporting reagent downhole, inserting or drawing analytical reagent into formation fluid to make a mixture of formation fluid and analytical reagent, and advancing the mixture through the cell of a spectral analyzer for downhole spectral analysis. A preferred embodiment uses a reagent container and an injector pump (syringe injector pump) for injecting reagent into the flow-line. Other embodiments use well bore overpressure to inject reagent into the flow-line with a restrictor or a throttle valve to control flow rate. This eliminates the need for an injector pump. Other embodiments use a fluid container with a syringe pump, a flow-line pump, or a step piston, to extract formation fluid from the flow-line, thereby inducing reagent injection into the flow-line.
As noted above, flow injection analysis is based on the injection of a liquid sample into a moving non-segmented continuous carrier stream of a suitable liquid. In contrast, the present invention involves downhole injection of reagent into a formation fluid sample.
Reagent-Injected-by-Syringe-Pump, Sample-Stopped Mode
Probe 21 is shown mounted to carriage 23 and penetrating mud cake 11. Resilient packer 25 provides a seal and inflow aperture 26 is in fluid communication with formation fluid. Resilient packer 25 seals inflow aperture 26 and flow-line 30 from well bore pressure. (Wellbore pressure is usually greater than formation pressure).
Flow-line 30 couples aperture 26 to spectral analyzer 41 via first flow-line isolation valve V1. It also provides an entry point for fluid injection of reagent from reagent container 31 via reagent container isolation valve V2. It also couples spectral analyzer 41 to flow-line pump 51, and, via second flow-line isolation valve V3, to main pump-out line 61.
Flow-line 30 has a cross-sectional area of approximately 0.2 cm2.
Reagent container 31 with injector pump 32 in the first preferred embodiment is provided as a syringe injector pump. Preferably, container 31 has a capacity of approximately four liters. The volume of reagent in a single injection is preferably in the range 2-10 cc.
Additional reagent containers, each having its own reagent container isolation valve V2, may be provided to increase reagent storage capacity or to provide the ability to select and inject an alternative reagent without withdrawing the formation tester from the wellbore. An auxiliary reagent container 31 a is shown dotted in
Spectral analyzer 41 is a conventional multi-channel (i.e. multi-wavelength) spectral analyzer, having a spectral analyzer cell 42, an illumination source 43, and an illumination detector 44. Spectral analyzer 41 has at least two channels, preferably more. Measuring pH requires a minimum of two channels. Optical density measurements are made simultaneously on all channels at the rate of at least three per second, preferably higher. To accommodate measurements of a wide range of target measured properties, the spectral analyzer preferably has ten channels, each channel measuring optical density at a different wavelength.
Flow-line pump 51 is a conventional dual-chamber piston pump.
Bypass valve V4 allows excess formation fluid to flow to main pump-out line 61 when reagent is injected into the otherwise stopped flow-line of the first preferred embodiment.
First Preferred Method, Reagent-Injected-by-Syringe-Pump, Sample-Stopped Mode
The first preferred embodiment of the method of the invention uses reagent injection spectral analysis operating in syringe-pumped-injection, sample-stopped mode. The method is summarized in the flowcharts of
Preferably, although not shown in
Step 414 of
The curves in
The graph of
In the present invention, a curve is selected whose peak lies between a smaller dilution factor value and a larger dilution factor value, outside of which the dilution factor is too small or too large for the specific analysis being attempted, or the signal to noise ratio is unacceptable.
The selection of an initial volume for execution of step 315 is not critical because adjusting the volume in accordance with steps 318 and 511-513 will produce a suitable value for volume to be inserted. For example, for a pH measurement of a moderately buffered sample using 0.04% phenol red reagent, and a sample flow-line velocity of 50 cm/sec, the 2 cc curve is selected from
Selection of the volume 2 cc ensures a relatively large number of valid pH measurements (acceptable dilution and good signal to noise ratio), in this case 6 measurements at the rate of 3 measurements per second. The corresponding dilution factor at the peak (11.5 read from the right-side scale) provides the basis for calculating the volume of reagent to be injected.
For a fluids analyzer in accordance with the preferred embodiment of the apparatus, the graph of
It would be possible to select the “5 cc” or higher volume curves and use measurements from two time windows (one before the peak and one after the peak) with acceptable dilution and signal to noise ratio but this would involve consuming more reagent.
The last step in
Optical density of the mixture in the cell of the spectral analyzer is measured to produce a time series of optical density values at multiple wavelengths. See
Because of uncertainties in the actual sample flow-line velocity and the actual reagent-sample mixing patterns in the downhole tool, it is recommended to adjust the volume of reagent to get a suitable dilution and an acceptable signal to noise ratio. See
The acceptable range will be different for different reagents and analytical procedures. As noted above, one or more auxiliary reagent containers may be included to provide the ability to select and inject an alternative reagent without requiring withdrawal of the formation tester from the wellbore.
Validated optical density values are stored as time series tables of spectral values. Then these tables of spectral values are used to produce an analysis of formation fluid using conventional spectral analysis techniques. See
The volume of reagent to be injected is determined by syringe pump rate and time. Preferably, the syringe pump rate is fixed, and adjusting the volume of reagent to be injected, involves adjusting an injection time. Alternatively, adjusting the volume of reagent to be injected includes adjusting the syringe pump rate.
Reagent-Injected-by-Syringe-Pump, Sample-Flowing Mode
The second embodiment of the invention is illustrated in
Reagent-Injected-by-Wellbore-Pressure, Uncontrolled, Sample-Stopped Mode
The third embodiment of the invention is illustrated in
The method of the third embodiment applies steps 315 and 316 of
Reagent-Injected-by-Wellbore-Pressure, Restrictor-Limited, Sample-Flowing Mode
The fourth embodiment of the method of the invention is illustrated in
Reagent-Injected-by-Wellbore-Pressure, Throttle-Controlled, Sample-Flowing Mode
The fifth embodiment of the method of the invention is illustrated in
Reagent-Injected-by-Sample-Extraction, Syringe-Pump, Sample-Stopped Mode
The sixth embodiment of the method of the invention is illustrated in
Reagent-Injected-by-Sample-Extraction, Main-Pump, Sample-Stopped Mode
The seventh embodiment of the method of the invention is illustrated in
Reagent-Injected-by-Sample-Extraction, Step-Piston, Sample-Stopped Mode
The eighth embodiment of the method of the invention is illustrated in
The pH of an unknown solution may be obtained spectroscopically using the equation below (R. G. Bates, Determination of pH: Theory and Practice, Chapter 6, John Wiley, 1964):
where Ka is the thermodynamic equilibrium constant for the pH sensitive dye (reagent) added to the sample and is a function of temperature; A and B are the respective fractions of the acid and base forms of the pH sensitive dye; and γA and γB are respective activity coefficients of the acid and base forms of the dye, and depend on ionic strength of the solution and temperature. Both Ka and activity coefficients could be weak functions of pressure as well.
The fraction of the dye that exists in the acid form (A) and base form (B) are measured spectroscopically. The pH calculation depends only on the ratio of B to A and is independent of the absolute concentration of the dye. The only constraint on the dye concentration in sample is that, depending on the buffering strength of the aqueous sample, there is an upper limit to the concentration of the dye beyond which the addition of the dye will affect the pH of the sample being measured. The lower limit on the dye concentration is set by the accuracy of the spectrophotometer and signal to noise ratio of the measurement. If the acid and base optical densities are very low, the poor signal to noise ratio will result in large errors in calculated pH. For typical formation waters and the optical detectors deployed in downhole formation tools, acceptable dye concentrations in fluid samples would typically fall in the range of 10−5M to 10−4M. The range of acceptable dilution factors, and hence the volume of dye to be injected, can be estimated as a function of the dye concentration in the reagent container and expected sample flow-line velocity using mixing curves such as shown in
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|U.S. Classification||436/28, 436/165, 436/164, 436/166|
|International Classification||E21B47/10, G01N21/00, G01N33/24, G01N21/03, G01N21/75, E21B49/08, G01N33/18|
|Cooperative Classification||E21B49/08, E21B47/1015, G01N33/18|
|European Classification||E21B49/08, E21B47/10G, G01N33/18|
|Feb 10, 2004||AS||Assignment|
Owner name: SCHLUMBERGER TECHNOLOGY CORPORATION, CONNECTICUT
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:TORGERSEN, TORLEIF;RAGHURAMAN, BHAVANI;HARRIGAN, EDWARD;AND OTHERS;REEL/FRAME:015004/0212;SIGNING DATES FROM 20030923 TO 20031211
|Mar 27, 2007||AS||Assignment|
Owner name: MOLECULAR IMPRINTS, INC., TEXAS
Free format text: RELEASE BY SECURED PARTY;ASSIGNOR:VENTURE LENDING & LEASING IV, INC.;REEL/FRAME:019072/0882
Effective date: 20070326
Owner name: MOLECULAR IMPRINTS, INC.,TEXAS
Free format text: RELEASE BY SECURED PARTY;ASSIGNOR:VENTURE LENDING & LEASING IV, INC.;REEL/FRAME:019072/0882
Effective date: 20070326
|Nov 16, 2010||CC||Certificate of correction|
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